Principles of mechanical Ventilation

A method to assist or replace spontaneous breathing using a machine.

Raw is the raw airway resistance that can be calculated using ∆P / V.

Airway resistance refers to conditions that impede airflow, increasing the work of breathing.

The amount of air delivered per breath, measured in liters.

The rate of air delivery, usually in liters per minute.

Work of breathing increases with ∆P and allows for flow changes; it decreases as ∆P decreases.

Compliance is a measure of lung expansion, calculated as Volume Change / Pressure Change (C = ∆V / ∆P).

The ability of the lungs to expand under pressure, defined as volume change per pressure change.

Dynamic compliance occurs during active breathing and is noted as Cdyn, using peak inspiratory pressure (PIP).

The force exerted on air within the lungs, associated with resistance.

Static compliance measures lung compliance without gas flow, such as during an inspiratory hold.

The opposition to airflow in the airways, defined as the change in pressure divided by flow.

A measure of the resistance air faces when flowing through the airways, calculated by change in pressure divided by flow.

C and ∆V are directly related; increasing compliance allows for increased volume without extra work.

Raw's change affects flow and pressure; higher Raw means increased pressure and lower flow.

C and ∆P have an inverse relationship; increased compliance reduces the work of breathing.

A measure of the lung's ability to stretch and expand. High compliance means easy expansion, low compliance means stiff lungs.

Indicates stiff lungs, which require more effort to expand. Common in conditions like fibrosis.

Indicates pliable lungs that expand easily, often seen in emphysema.

The phenomenon where lung compliance differs during inspiration and expiration for the same volume.

A graphical representation of lung pressure and volume changes. Shifts indicate compliance changes.

Elastance is the measure of a material's ability to return to original shape after deformation, represented mathematically as E = ∆P / ∆V.

Elasticity describes the tendency of a material to resist stretching and maintain its shape when force is applied.

Normal compliance refers to the ability of the lungs to expand, measured as 50-100 mL/cmH2O.

Normal resistance is the opposition to airflow in the lungs, typically 1-8 cmH2O/L/s.

Dead space ventilation is the part of a breath that does not participate in gas exchange, signifying ventilation without perfusion.

Anatomic dead space refers to the volume of air in the conducting zones of the respiratory tract, about 2 mL/kg in upright position.

Alveolar dead space is gas in unperfused alveoli, typically negligible in healthy individuals.

Physiologic dead space is the total of anatomic and alveolar dead spaces and usually accounts for 20-40% of tidal volume.

A condition where breathing is insufficient to maintain adequate oxygenation or carbon dioxide removal; caused by various factors.

Decreased breathing rate that leads to increased carbon dioxide levels (PaCO2) in the blood.

An imbalance in ventilation (V) and perfusion (Q), leading to ineffective gas exchange.

The passage of blood through the lungs without participating in gas exchange, causing hypoxemia.

Impaired gas exchange due to thickened alveolar-capillary membranes or reduced surface area.

Severe hypoxemia despite high levels of oxygen administered (PaO2 < 40 mm Hg).

Partial pressure of oxygen in arterial blood, indicating oxygen levels available for use by the body.